Sorption and desorption of imidazolium based ionic liquids in different soil types

Biodegradation of Choline NTF2 by Pantoea agglomerans in Different Osmolarity. Characterization and Environmental Implications of the Produced Exopolysaccharide

A specific microorganism, Pantoea agglomerans uam8, was isolated from the ionic liquid (IL) Choline NTF2 and identified by molecular biology. A biodegradation study was performed at osmolarity conditions (0.2, 0.6, 1.0 M). These had an important influence on the growth of the strain, exopolysaccharide (EPS) production, and biodegradation (1303 mg/L max production and 80% biodegradation at 0.6 M). These conditions also had an important influence on the morphology of the strain and its EPSs, but not in the chemical composition. The EPS (glucose, mannose and galactose (6:0.5:2)) produced at 0.6 M was further characterized using different techniques. The obtained EPSs presented important differences in the behavior of the emulsifying activity for vegetable oils (olive (86%), sunflower (56%) and coconut (90%)) and hydrocarbons (diesel (62%), hexane (60%)), and were compared with commercial emulsifiers. The EPS produced at 0.6 M had the highest emulsifying activity overall. This EPS did not show cytotoxicity against the tested cell line (<20%) and presented great advantages as an antioxidant (1,1-diphenyl-2-picryl-hydrazyl radical (DPPH) (85%), hydroxyl radical (OH) (99%), superoxide anion (O2-) (94%), chelator (54%), and antimicrobial product (15 mm). The osmolarity conditions directly affected the capacity of the strain to biodegrade IL and the subsequently produced EPS. Furthermore, the EPS produced at 0.6 M has potential for environmental applications, such as the removal of hazardous materials by emulsification, whilst resulting in positive health effects such as antioxidant activity and non-toxicity.

Toward the Proactive Design of Sustainable Chemicals: Ionic Liquids as a Prime Example

The tailorable and often unique properties of ionic liquids (ILs) drive their implementation into a broad variety of seminal technologies. The modular design of ILs allows in this context a proactive selection of structures that favor environmental sustainability─ideally without compromising their technological performance. To achieve this objective, the whole life cycle must be taken into account and various aspects considered simultaneously. In this review, we discuss how the structural design of ILs affects their environmental impacts throughout all stages of their life cycles and scrutinize the available data in order to point out knowledge gaps that need further research activities. The design of more sustainable ILs starts with the selection of the most beneficial precursors and synthesis routes, takes their technical properties and application specific performance into due account, and considers its environmental fate particularly in terms of their (eco)toxicity, biotic and abiotic degradability, mobility, and bioaccumulation potential. Special emphasis is placed on reported structure-activity relationships and suggested mechanisms on a molecular level that might rationalize the empirically found design criteria.

Enzymatic Activity and Its Relationship with Organic Matter Characterization and Ecotoxicity to Aliivibrio fischeri of Soil Samples Exposed to Tetrabutylphosphonium Bromide

This study aimed to determine the impact of tetrabutylphosphonium bromide [TBP][Br] on the soil environment through an experiment on loamy sand samples. The tested salt was added to soil samples at doses of 0 (control), 1, 10, 100, and 1000 mg kg-1 dry matter (DM). During the experiment, the activity of selected enzymes involved in carbon, phosphorus, and nitrogen cycles, characteristics of organic matter with Fourier-transform infrared (FT-IR) spectroscopy, and toxicity of soil samples in relation to Aliivibrio fischeri were determined at weekly intervals. The results showed that low doses of [TBP][Br] (1 and 10 mg kg-1 DM) did not have much influence on the analyzed parameters. However, the addition of higher doses of the salt into the soil samples (100 and 1000 mg kg-1 DM) resulted in a decrease in the activity of enzymes participating in the carbon and phosphorus cycle and affected the activation of those enzymes involved in the nitrogen cycle. This may be due to changes in aerobic conditions and in the qualitative and quantitative composition of soil microorganisms. It was also observed that the hydrophobicity of soil organic matter was increased. Moreover, the findings suggested that the soil samples containing the highest dose of [TBP][Br] (1000 mg kg-1 DM) can be characterized as acute environmental hazard based on their toxicity to Aliivibrio fischeri bacteria. The increased hydrophobicity and ecotoxicity of the soil samples exposed to the tested salt were also positively correlated with the activity of dehydrogenases, proteases, and nitrate reductase. Observed changes may indicate a disturbance of the soil ecochemical state caused by the presence of [TBP][Br].

Ionic liquids as environmental hazards - Crucial data in view of future PBT and PMT assessment

Ionic liquids (ILs) constitute a large group of chemical compounds. They have gained much attention among scientists and industry due to their unique properties. Due to the fact that ILs are purely ionic compounds, there is the possibility to design an enormous number of cation and anion combinations, making them designer solvents. Thus it also creates the possibility of producing more environmentally benign solvents. However, significant drawbacks related mainly to their toxicity and persistence have already been noticed. Furthermore the interest in these compounds is constantly growing and their impact on the environment should be defined. More and more ILs are produced or imported in the amount higher than 10 tonnes per year and the group of ILs registered in REACH is still expanding. Thus for an increasing number of compounds, it will be necessary to perform a PBT and PMT assessment using the criteria described in REACH. Therefore the data collected in this work thoroughly sort out the information on the toxicity, bioconcentration/bioaccumulation, biodegradation and mobility of ILs in the context of PBT and PMT assessment.

Chemometrics for Selection, Prediction, and Classification of Sustainable Solutions for Green Chemistry—A Review

In this review, we present the applications of chemometric techniques for green and sustainable chemistry. The techniques, such as cluster analysis, principal component analysis, artificial neural networks, and multivariate ranking techniques, are applied for dealing with missing data, grouping or classification purposes, selection of green material, or processes. The areas of application are mainly finding sustainable solutions in terms of solvents, reagents, processes, or conditions of processes. Another important area is filling the data gaps in datasets to more fully characterize sustainable options. It is significant as many experiments are avoided, and the results are obtained with good approximation. Multivariate statistics are tools that support the application of quantitative structure–property relationships, a widely applied technique in green chemistry.

Ionic Liquids Toxicity-Benefits and Threats

Ionic liquids (ILs) are solvents with salt structures. Typically, they contain organic cations (ammonium, imidazolium, pyridinium, piperidinium or pyrrolidinium), and halogen, fluorinated or organic anions. While ILs are considered to be environmentally-friendly compounds, only a few reasons support this claim. This is because of high thermal stability, and negligible pressure at room temperature which makes them non-volatile, therefore preventing the release of ILs into the atmosphere. The expansion of the range of applications of ILs in many chemical industry fields has led to a growing threat of contamination of the aquatic and terrestrial environments by these compounds. As the possibility of the release of ILs into the environment s grow systematically, there is an increasing and urgent obligation to determine their toxic and antimicrobial influence on the environment. Many bioassays were carried out to evaluate the (eco)toxicity and biodegradability of ILs. Most of them have questioned their "green" features as ILs turned out to be toxic towards organisms from varied trophic levels. Therefore, there is a need for a new biodegradable, less toxic "greener" ILs. This review presents the potential risks to the environment linked to the application of ILs. These are the following: cytotoxicity evaluated by the use of human cells, toxicity manifesting in aqueous and terrestrial environments. The studies proving the relation between structures versus toxicity for ILs with special emphasis on directions suitable for designing safer ILs synthesized from renewable sources are also presented. The representants of a new generation of easily biodegradable ILs derivatives of amino acids, sugars, choline, and bicyclic monoterpene moiety are collected. Some benefits of using ILs in medicine, agriculture, and the bio-processing industry are also presented.

Searching for Solvents with an Increased Carbon Dioxide Solubility Using Multivariate Statistics

Ionic liquids (ILs) are used in various fields of chemistry. One of them is CO₂ capture, a process that is quite well described. The solubility of CO₂ in ILs can be used as a model to investigate gas absorption processes. The aim is to find the relationships between the solubility of CO₂ and other variables—physicochemical properties and parameters related to greenness. In this study, 12 variables are used to describe a dataset consisting of 26 ILs and 16 molecular solvents. We used a cluster analysis, a principal component analysis, and a K-means hierarchical clustering to find the patterns in the dataset and the discriminators between the clusters of compounds. The results showed that ILs and molecular solvents form two well-separated groups, and the variables were well separated into greenness-related and physicochemical properties. Such patterns suggest that the modeling of greenness properties and of the solubility of CO₂ on physicochemical properties can be difficult.

Structural effect of imidazolium-type ionic liquid adsorption to montmorillonite

The adsorption of 1-alkyl-3-methylimidazolium-type ionic liquids (ITILs) coupled with different counteranions (Tf₂N^-, PF₆^-, BF₄^-, and Cl^-) with variational cation alkyl chain lengths (n = 2, 4, 6, and 8) to montmorillonite was investigated to explore the structural effect of ITILs on their adsorption. A series of montmorillonite with different cation exchange capacities (CECs) and possessing a set of homoionic K- and Cs-exchanged interlayer cations were also examined to assess the influence of montmorillonite structure and characteristics. The adsorption of ITILs to Na-saturated montmorillonite (Na-MAz) was counteranion-independent but increased with the increase in the alkyl chain length of the imidazolium cation. X-ray diffraction results indicated that ITIL cations with different alkyl chains lay flat between the montmorillonite interlayers with different contact angles. The uptake of ITILs by Na-MAz increased with the increase in the solution pH and decrease in ionic strength. Na-MAz exhibited greater adsorption than K- and Cs-saturated MAz due to the larger hydrated radii of Na⁺ than those of K⁺ and Cs⁺. The uptake of ITILs to Na-MZj (CEC = 64 mmol/100 g) was almost half compared with that of Na-MAz (CEC = 117 mmol/100 g). Consequently, this work demonstrated that the ITIL adsorption to montmorillonite was dependent on the structures of both adsorbate and adsorbent.

Preparation of ionic liquids/montmorillonite composites and its application for diclofenac sodium removal

Ionic liquid (IL) is an environment friendly organic solvent, which has a relatively low vapor pressure. This work focuses on adsorption of montmorillonite (Mt) to IL as well as removal of diclofenac sodium (DS), an anionic contaminant in water, by IL-modified Mt. The experiment shows absorption of DS increased by increasing IL dosage in modifying Mt. As a result, to modified Mt. with a concentration of IL of 200% cationic exchange capacity (CEC), its static absorption of modified Mt. to DS is 310 mmol/kg, with a rapid rate (reaching balance in 5 min). In dynamic column experiment, absorption of DS reaches balance after 24 h, which absorption amount is 2490 mmol/kg. It can be inferred that modification of IL change surface charge of Mt. and renders intercalation of DS into Mt. interlayers, thus increasing adsorption capacity to DS. These features could further expand the application of ILs and enable IL-modified Mt. to be used as inexpensive sorbents for the removal of chromate and other oxyanions from water.

Recovery and purification of ionic liquids from solutions: a review

With low melting point, extremely low vapor pressure and non-flammability, ionic liquids have been attracting much attention from academic and industrial fields. Great efforts have been made to facilitate their applications in catalytic processes, extraction, desulfurization, gas separation, hydrogenation, electronic manufacturing, etc. To reduce the cost and environmental effects, different technologies have been proposed to recover the ionic liquids from different solutions after their application. This review is mainly focused on the recent advances of the recovery and purification of ionic liquids from solutions. Several methods for recovery of ionic liquids including distillation, extraction, adsorption, membrane separation, aqueous two-phase extraction, crystallization and external force field separation, are introduced and discussed systematically. Some industrial applications of ionic liquid recovery and purification methods are selected for discussion. Additionally, considerations on the combined design of different methods and process optimization have also been touched on to provide potential insights for future development of ionic liquid recovery and purification.

Removal of Ionic Liquids from Oil Sands Processing Solution by Ion-Exchange Resin

Ionic liquids (ILs) have been reported to be good process aids for enhanced bitumen recovery from oil sands. However, after the extraction, some ionic liquids are left in the residual solids or solutions. Herein, a washing–ion exchange combined method has been designed for the removal of two imidazolium-based ILs, ([Bmim][BF4] and [Emim][BF4]), from residual sands after ILs-enhanced solvent extraction of oil sands. This process was conducted as two steps: water washing of the residual solids to remove ILs into aqueous solution; adsorption and desorption of ILs from the solution by the sulfonic acid cation-exchange resin (Amberlite IR 120Na). Surface characterization showed that the hydrophilic ionic liquids could be completely removed from the solid surfaces by 3 times of water washing. The ionic liquids solution was treated by the ion-exchange resin. Results showed that more than 95% of [Bmim][BF4] and 90% of [Emim][BF4] could be adsorbed by the resins at 20 °C with contact time of 30 min. The effects of some typical coexisted chemicals and minerals, such as salinity, kaolinite (Al4[Si4O10](OH)8), and silica (SiO2), in the solution on the adsorption of ionic liquids have also been investigated. Results showed that both kaolinite and SiO2 exerted a slight effect on the uptake of [Bmim][BF4]. However, it was observed that increasing the ionic strength of the solution by adding salts would deteriorate the adsorption of [Bmim]+ on the resin. The adsorption behaviors of two ILs fit well with the Sips model, suggesting the heterogeneous adsorption of ionic liquids onto resin. The adsorption of ionic liquids onto Amberlite IR 120Na resin was found to be pseudo-second-order adsorption. The regeneration tests showed stable performance of ion-exchange resins over three adsorption–desorption cycles.

Counteranion-dependent sorption of imidazolium- and benzimidazolium-based ionic liquids by soot

Sorption of ionic liquids (ILs) to soil and porous materials as affected by anions was observed, but scarce effort has been focused on addressing the role of counteranions in sorption and the associated underlying mechanisms. In this work, two series of 1-butyl-3-methylimidazolium- (Bmim-) and N-butyl, methyl-benzimidazolium-based (Bmbim-based) ILs coupled with different counteranions were prepared to investigate the effect of anions on IL sorption by soot. The octanol-water partition coefficient (K_ow) and the ion-pair formation constant at infinite dilution in water (K_IP^°) of ILs were independently measured to explore the contribution of counteranion-dependent hydrophobicity and ion-pair. A wide range of sorption coefficients (K_d) of ILs were achieved with values varying from 59.8 to 344.3 L·kg^-1 for Bmbim-based ILs and from 253.4 to 489.7 L kg^-1 for Bmbim-based ILs. Compared with other anions, bis(trifluoromethanesulphonyl)imide ([Tf₂N]^-) and hexafluorophosphate ([PF₆]^-) exhibit tighter association with IL cations in aqueous solution due to their larger K_ow and higher K_IP^°. Positive linear relationships between log K_IP^° and K_d and between log K_ow and K_d evidenced that the counteranion-dependent sorption of ILs relies on the association strengths of IL cations and counteranions, which further influence the hydrophobicity/hydrophilicity of ion pairs. Compared with that of strongly coordinating anions (such as [CH₃SO₃]^-, [CF₃COO]^-, [BF₄]^-, [CF₃SO₃]^-, and [Cl]^-), the addition of weakly coordinating anions (such as [Tf₂N]^- and [PF₆]^-) in solution contributes to markedly large sorption enhancement of ILs. Consequently, the contribution of different counteranions on IL sorption is essentially based on the formation of ion pair with different K_IP^° and K_ow in aqueous solution.

Assessment of the photocatalytic transformation of pyridinium-based ionic liquids in water

We studied some ionic liquids (ILs) belonging to the pyridinium class under photocatalytic treatment. In particularly, we analysed how the length of the alkyl chain, the kind of inorganic ion and the type of substituents could influence the disappearance rate, the mineralization extent, the acute toxicity and the transformation mechanism. For such, we selected some pyridinium derivatives with different alkyl chain but the same anion, namely tetrafluoroborate (1-ethylpyridinium, 1-butylpyridinium, 1-hexylpyridinium), with two alkyl substituents (4-methyl-1-butylpyridinium) and with a different substituent (1-cyanopropylpyridinium). Then, on a selected IL (1-butylpyridinium), we evaluate the role of different inorganic anions (bromine and chlorine). The results show that irrespective to the alkyl chain or the number of substituents, the transformation involved an attack to the alkyl chain, proceeded through the formation of harmless compounds and the mineralization was easily achieved within 4h. Nitrogen was mainly released as ammonium ion. When introducing a cyano group, the extent of nitrate ions and the number of possible transformation route increased. Conversely, the type of inorganic ion deeply affected the transformation pathways and the extent of mineralization. Actually, in the presence of bromide as anion, IL was only partially mineralized and the formation of highly persistent transformation products occurred.

Evaluation of risk assessment of new industrial pollutant, ionic liquids on environmental living systems

Ionic liquids (ILs) are much known for their promising alternative for volatile solvents in industries and gained popularity as a greener solvent, however industrial effluent discharge containing ILs are also increasing. There is a scarcity of information on the toxicity of ILs; the present study will explore different facts about their harmfulness. The toxic effects of five different ILs: [C₄MIM]Br, [Hx₃PC₁₄]N(CN)₂, [C₁₀MIM]BF₄, [BTDA]Cl and [C₄MPY]Cl were analysed on bacteria, fungi, plant and animal cells. Both Gram positive and negative bacteria were found to be more susceptible to [C₁₀MIM]BF₄ and [BTDA]Cl than [C₄MIM]Br, [Hx₃PC₁₄]N(CN)₂ and [C₄MPY]Cl, whereas fungi revealed quite a resistance to all ILs. All ILs were toxic towards Triticum aestivum affecting their roots and shoots, however [C₁₀MIM]BF₄ and [BTDA]Cl were more toxic amongst them. Studies on Allium cepa described their toxic behaviour at the genetic level by altering cell division and nuclear material. Furthermore, studies on human red blood cells described by % haemolysis in which [Hx₃PC₁₄]N(CN)₂ and [BTDA]Cl exhibited higher toxicity at very lower concentrations. While the genotoxic effect on blood lymphocytes exerted by [Hx₃PC₁₄]N(CN)₂, [C₁₀MIM]BF₄ and [BTDA]Cl confirmed their toxic effects on human cells.

Interaction between Dissolved Organic Matter and Long-Chain Ionic Liquids: A Microstructural and Spectroscopic Correlation Study

The production and use of ionic liquids (ILs) increase the potential risk after their emission into the environment. After entering the environment, ILs will readily interact with dissolved organic matter (DOM), and their environmental behavior will be impacted by DOM, which is abundant in the environment and has various functional groups. However, to date, the interaction between DOM and ILs, especially long-chain ILs, remains unclear. In this work, the interaction between long-chain ILs and humic acid (HA), a representative DOM, was investigated using synchronous fluorescence, Fourier transform infrared spectroscopy, dynamic light scattering, and zeta potential techniques, which were integrated with two-dimensional correlation spectroscopy (2DCOS), hetero-2DCOS, and perturbation-correlation moving-window analyses. The results show that cation exchange by the carboxylic groups in humic-like fractions was primarily responsible for interaction at low IL concentrations. As a result, the decrease in electrostatic repulsion and the increase in hydrophobicity facilitated the loose aggregation of HA. With an increase in IL concentration, the aromatic and carbonyl groups were involved in the interaction via the π-π interaction and dipole-dipole interaction, respectively, which resulted in the disruption of the intramolecular hydrogen bond and promoted the compaction of HA under the hydrophobic effect. The intensity transition sequence of various groups in HA was elucidated more specifically by 2DCOS. With these results, a comprehensive view of the structural changes of DOM in its IL-binding process was obtained, and the fate and environmental impact of ILs could be better understood. Furthermore, the superior potential of such an integrated approach in investigating the complex interactions in the environment was also demonstrated.

Assessment of ionic liquids' toxicity through the inhibition of acylase I activity on a microflow system

Acylase I (ACY I) plays a role in the detoxication and bioactivation of xenobiotics as well in other physiological functions. In this context, an automated ACY I assay for the evaluation of ionic liquids' (ILs) toxicity was developed. The assay was implemented in a sequential injection analysis (SIA) system and was applied to eight commercially available ILs. The SIA methodology was based on the deacetylation of N-acetyl-l-methionine with production of l-methionine, which was determined using fluorescamine. ACY I inhibition in the presence of ILs was monitored by the decrease of fluorescence intensity. The obtained results confirmed the influence of ILs' structural elements on its toxicity and revealed that pyridinium and phosphonium cations, longer alkyl side chains and tetrafluoroborate anion displayed higher toxic effect on enzyme activity. The developed methodology proved to be robust and exhibited good repeatability (RSD < 1.3%, n = 10), leading also to a reduction of reagents consumption and effluents production. Thus, it is expected that the proposed assay can be used as a novel tool for ILs' toxicity screening.

Life-Cycle Perspectives on Aquatic Ecotoxicity of Common Ionic Liquids

This study compares the aquatic ecotoxicity impacts of production- and use-phase release of five common ionic liquids (ILs). Integrating toxicity data, physical properties, and fate and transport parameters with the USEtox model, we report, for the first time, the freshwater ecotoxicity characterization factors for [Bmim](+)[Br](-), [Bmim](+)[Cl], [Bmim](+)[BF4](-), [Bmim](+)[PF6](-), and [BPy](+)[Cl](-) as 624, 748, 823, 927, and 1768 CTUe/kg, respectively. IL Production life cycle inventories were modeled and utilized to estimate their production-side ecotoxicity impacts. Literature on environmental aspects of ILs propagates either their green characteristics (no air emissions and high recyclability) or their nongreen aspects due to toxicity concerns of their release to water. This study adds a third dimension by showing that the upstream ecotoxicity impacts of producing ILs could outweigh the potential ecotoxicity impacts of direct release during use. Furthermore, for the studied ILs, an average of 83% of ecotoxicity impacts associated with their production can be linked to chemicals and materials released during the upstream synthesis steps, while only 17% of ecotoxicity impacts relate to life-cycle energy consumption. The findings underscore the need to develop sustainable synthesis routes, tight control over chemical releases during production, and careful selection of precursor materials and production processes.

Automated cytochrome c oxidase bioassay developed for ionic liquids' toxicity assessment

A fully automated cytochrome c oxidase assay resorting to sequential injection analysis (SIA) was developed for the first time and implemented to evaluate potential toxic compounds. The bioassay was validated by evaluation of 15 ionic liquids (ILs) with distinct cationic head groups, alkyl side chains and anions. The assay was based on cytochrome c oxidase activity reduction in presence of tested compounds and quantification of inhibitor concentration required to cause 50% of enzyme activity inhibition (EC50). The obtained results demonstrated that enzyme activity was considerably inhibited by BF4 anion and ILs incorporating non-aromatic pyrrolidinium and tetrabutylphosphonium cation cores. Emim [Ac] and chol [Ac], on contrary, presented the higher EC50 values among the ILs tested. The developed automated SIA methodology is a simple and robust high-throughput screening bioassay and exhibited good repeatability in all the tested conditions (rsd<3.7%, n=10). Therefore, it is expected that due to its simplicity and low cost, the developed approach can be used as alternative to traditional screening assays for evaluation of ILs toxicity and identification of possible toxicophore structures. Additionally, the results presented in this study provide further information about ILs toxicity.

Environmental Application, Fate, Effects, and Concerns of Ionic Liquids: A Review

Ionic liquids (ILs) comprise mostly of organic salts with negligible vapor pressure and low flammability that are proposed as replacements for volatile solvents. ILs have been promoted as "green" solvents and widely investigated for their various applications. Although the utility of these chemicals is unquestionable, their toxic effects have attracted great attention. In order to manage their potential hazards and design environmentally benign ILs, understanding their environmental behavior, fate and effects is important. In this review, environmentally relevant issues of ILs, including their environmental application, environmental behavior and toxicity are addressed. In addition, also presented are the influence of ILs on the environmental fate and toxicity of other coexisting contaminants, important routes for designing nontoxic ILs and the techniques that might be adopted for the removal of ILs.

A comparative study of the terrestrial ecotoxicity of selected protic and aprotic ionic liquids

Ionic liquids (ILs) are a fairly new and very promising group of compounds with a vast variety of possible structures and uses. They are considered to be potentially "green", but their impact on the environment tends to be neglected or not studied enough, especially when it comes to terrestrial ecotoxicity, where there are very few studies performed to date. This work presents a comparative study of the terrestrial ecotoxicity of selected representatives of two ILs groups: a new family of protic ILs (derived from aliphatic amines and organic acids) and some frequently used aprotic ILs (substituted imidazolium and piridinium chlorides). Toxicity of the ILs towards three terrestrial plant species (Allium cepa, Lolium perenne and Raphanus sativus) and soil microorganisms involved in carbon and nitrogen transformation was analyzed. Protic ILs have shown no toxic effect in most of the tests performed. The EC50 values for aprotic ILs are various orders of magnitude lower than the ones for protic ILs in all of the tests. The most toxic ILs are the most complex ones in both of the analyzed groups. Protic ILs seem to have a potential for biodegradation in soil, while aprotic ILs exhibit inhibitory effects towards the carbon transforming microbiota. These findings indicate that protic ILs can be considered as less toxic and safer for the terrestrial environment than the aprotic ILs.

Modification of a Ca-montmorillonite with ionic liquids and its application for chromate removal

Ionic liquids (ILs), due to their low vapor pressure, have been explored as green solvents for organic synthesis. In this study, the uptake of ILs on a high charge Ca-montmorillonite (MMT) and the use of the IL-modified MMT for the removal of anionic contaminants from water were systematically studied. Uptake of ILs by MMT was exclusively resulted from a cation exchange mechanism when the initial IL concentrations were less than the critical micelle concentration (CMC) and the sorbed ILs formed a monolayer conformation on the surface of MMT. When the initial IL concentrations were greater than the CMC, both cation exchange and hydrophobic interactions were responsible for the IL uptake. The IL molecules formed admicelles and the surface charge was reversed to positive balanced by counterion Cl(-) when the IL loading was higher than the cation exchange capacity of the mineral. The modified MMT could remove chromate from water instantaneously, with an adsorption capacity of 190 mmol/kg and a 99.5% removal efficiency at an initial chromate concentration of 2.6 mmol/L. These features could further expand the application of ILs and enable IL-modified MMT to be used as inexpensive sorbents for the removal of chromate and other oxyanions from water.

A brief overview of the potential environmental hazards of ionic liquids

Over past decades ionic liquids, a promising alternative to traditional organic solvents, have been dramatically expanding in popularity as a new generation of chemicals with potential uses in various areas in industry. In the literature these compounds have often been referred to as environmentally friendly; however, in recent years the perception of their greenness dramatically changed as the scientific community began to proactively assess the risk of their application based on the entire life-cycle. This review gives a brief overview of the current knowledge regarding the potential risks linked to the application of ionic liquids - from preparation to their disposal, with special emphasis on their potential environmental impacts and future directions in designing inherently safer ionic liquids.

Interaction of Novel Ionic Liquids with Soils

With the constant development of new ionic liquids, the understanding of the chemical fate of these compounds also needs to be updated. To this effect, the interaction of a number of novel ionic liquids with soils was determined. Therefore, three novel headgroups (ammonium, phosphonium, or pyrrolidinium) with single or quaternary substitution were tested on a variety of soils with high-to-low organic matter content and high-to-low cation exchange capacity, thereby trying to capture the full range of possible soil interactions. It was found that the ionic liquids with single butyl alkyl chain interacted more strongly with the soils (especially with a higher cation exchange capacity), at lower concentrations, than the quad-substituted ionic liquids. However, the quad-substituted ionic liquids interacted more strongly at higher concentrations, due to the double-layer formation, and induced stronger dipole interaction with previously sorbed molecules.

Sorption of ionic liquids onto soils: experimental and chemometric studies

Chemometric analyses are a great tool to support typical experimental studies of the interactions of xenobiotics with natural environment. Such interpretations are able to determine statistically significant correlations and finally lead to identification of the major sorption factors. However, to effectively use chemometrics a bigger data set is required. Even though the ionic liquids are intensively studied, their complete fate or prediction of their behavior in the natural environment is still unclear. Therefore, to evaluate and distinguish the patterns of interactions of ILs in soil environment by chemometrics, sorption of nine ionic liquids (imidazolium and pyridinium chlorides) on 11 types of various soils was tested. Experimental studies indicated that compounds with longer alkyl side chains were sorbed far more strongly than weakly lipophilic ones. Moreover, salts with short and/or hydroxylated derivatives were more mobile in soils/sediments and thus, might cause a danger of contamination of surface or ground waters. Cluster analysis revealed that ionic liquids form two major clusters according to interaction with soil surface - one grouping compounds with short and hydroxylated alkyl side chains and the second with the rest of compounds. Pairwise scatterplots for correlations between soil variables and sorption coefficients indicated that the main soil parameter responsible for the sorption was cation exchange capacity. Correlation of sorption coefficients, K(d), with pH indicated the existence of lower sorption potency in lower pH values.

Sorption to dissolved humic acid and its impacts on the toxicity of imidazolium based ionic liquids

Two typical ionic liquids (ILs), 1-butyl-3-methylimidazolium chloride ([C4MIM]Cl) and 1-octyl-3-methylimidazolium chloride ([C8MIM]Cl), are demonstrated to associate strongly with dissolved organic matter (DOM) with distribution coefficients (KDOC) in the range of 10(4.2) to 10(4.6) for Aldrich humic acid (used as model DOM). With the increase of humic acid concentration to 11 μg/mL DOC (dissolved organic carbon), the free fraction (ratio of freely dissolved to total concentration) of [C4MIM]Cl and [C8MIM]Cl reduced to about 0.85 and 0.79, respectively. This reduction of freely dissolved concentration gave rise to remarkable reduction of bioavailability and toxicity of the two ILs. MTT assay with HepG2 cell lines showed that the EC50 values were 459 μmol/L for [C4MIM]Cl and 12 μmol/L for [C8MIM]Cl, respectively, and the cell viability increased about 50% in the presence of trace amount of humic acid (1 μg/mL DOC). The SOS/umu test indicated mutagenicity for [C4MIM]Cl at levels above 664 μmol/L, and the genotoxicity was diminished with the addition of trace humic acid (0.00000374-0.374 μg/mL DOC). The studied ILs showed acute toxicity toward model fish medaka with a 96 h median lethal concentration (LC50) of 2254 μmol/L for [C4MIM]Cl and 366 μmol/L for [C8MIM]Cl. The addition of humic acid (5.49 μg/mL DOC for [C8MIM]Cl, 1.37 μg/mL DOC for [C4MIM]Cl) to IL solutions reduced the death rate of medaka to a minimum value of ∼25% of that at zero DOC. Our results suggest that DOM may play an important role in determining the environmental fate and toxicity of imidazolium-based ILs, and its effects should be taken into account in assessing the environmental risk of ILs.

Ionic liquids: a pathway to environmental acceptability

Ionic liquids were initially proposed as replacements for conventional organic solvents; however, their chemistry has developed remarkably and offers unexpected opportunities in numerous fields, ranging from electrochemistry to biology. As a consequence of ionic liquids advancing towards potential and actual applications, a comprehensive determination of their environmental, health and safety impact is now required. This critical review aims to present an overview of the current understanding of the toxicity and environmental impact of the principal ionic liquid groups, and highlights some emerging concerns. Each cation type is considered separately, examining the significance of the biological data, and identifying the most critical questions, some yet unresolved. The need for more, and more detailed, studies is highlighted (176 references).

Environmental fate and toxicity of ionic liquids: a review

Ionic liquids (ILs) are organic salts with low melting point that are being considered as green replacements for industrial volatile organic compounds. The reputation of these solvents as "environmental friendly" chemicals is based primarily on their negligible vapor pressure. Nonetheless, the solubility of ILs in water and a number of literature documenting toxicity of ILs to aquatic organisms highlight a real cause for concern. The knowledge of ILs behavior in the terrestrial environment, which includes microbial degradation, sorption and desorption, is equally important since both soil and aquatic milieu are possible recipients of IL contamination. This article reviews the achievements and current status of environmental risk assessment of ILs, and hopefully provides insights into this research frontier.

Biodegradation of diesel fuel by a microbial consortium in the presence of 1-alkoxymethyl-2-methyl-5-hydroxypyridinium chloride homologues

Fast development of ionic liquids as gaining more and more attention valuable chemicals will undoubtedly lead to environmental pollution. New formulations and application of ionic liquids may result in contamination in the presence of hydrophobic compounds, such as petroleum mixtures. We hypothesize that in the presence of diesel fuel low-water-soluble ionic liquids may become more toxic to hydrocarbon-degrading microorganisms. In this study the influence of 1-alkoxymethyl-2-methyl-5-hydroxypyridinium chloride homologues (side-chain length from C(3) to C(18)) on biodegradation of diesel fuel by a bacterial consortium was investigated. Whereas test performed for the consortium cultivated on disodium succinate showed that toxicity of the investigated ionic liquids decreased with increase in side-chain length, only higher homologues (C(8)-C(18)) caused a decrease in diesel fuel biodegradation. As a result of exposure to toxic compounds also modification in cell surface hydrophobicity was observed (MATH). Disulphine blue active substances method was employed to determine partitioning index of ionic liquids between water and diesel fuel phase, which varied from 1.1 to 51% for C(3) and C(18) homologues, respectively. We conclude that in the presence of hydrocarbons acting as a solvent, the increased bioavailability of hydrophobic homologues is responsible for the decrease in biodegradation efficiency of diesel fuel.